Digital data transmission systems are well-known in which large numbers of individual users are connected by shared transmission facilities to a centralized information processing facility. It is common in such systems to communicate between terminals and the central processor by using messages having header portions with address information and data portions of variable length. Moreover, in modern systems, terminals normally have cathode ray display tubes on which the data portion of the message is displayed in order to be read by the user.
Many messages include very long data portions to be displayed, exceeding the capacity of a single screen on the cathode ray tube. In accordance with standard message protocol, such messages include check characters which allow the receiving terminal to ascertain if the message is error-free. If an error has occurred, a request message is sent to have the erroneous message retransmitted. It is only after an error-free message is received and stored locally in the user's terminal that the message is displayed on the CRT screen.
One major problem in multiuser systems such as that described above is the slow response time of the system. Competition for access to the data base and competition for the shared transmission facilities account for some of the delayed response. These contributions can be minimized by good system design which provides adequate capacity in the shared facilities. One source of delayed response time which is, at least in part, determined by user options is the time required to insure the reception of a complete error-free multiscreen message. The delay involved in waiting for the complete message and insuring that no errors have occurred can assume a significant proportion of the total response time and, indeed, in some systems can dominate the response time.
Such long messages can, of course, be broken down into smaller units and thereby speed up the response time. However, a larger number of smaller units increases the overhead time required to process the message segments and may, at least in some cases, increase rather than reduce the total response time.
The problem, then, is to improve the response time for the transmission reception and display if multipage or multiscreen messages from a centralized data processor and transmitted to the ultimate user over shared transmission facilities.